A narrow-band filter, is subdivided from a band-pass filter. The definition of the narrow-band filter is the same as the band-pass filter, which means that the filter allows optical signals to pass in a particular band and optical signals deviating from this band on both sides are blocked. A passband of the narrow-band filter is relatively narrow, and is used in fields such as unmanned vehicle position imaging technology and face recognition technology (facial feature information recognition).
The unmanned vehicle technology and face recognition technology of intelligent devices have been popular. For example, the interference lights when capturing vehicle plates mainly contain sun lights, including direct sun lights and diffused sun lights or scattered sun lights, as well as headlights of a car, including halogen lights, xenon lights and LED lights, in addition to some road lights, such as high pressure sodium lights or incandescent lights and so on. The sources of interference lights are complex, involve a wide wavelength range, and span even more than CCD spectral response range of 400-1100 nm. Furthermore, the interference intensity is also stronger. Hence, it is not easy to remove the interference lights when capturing the plates. The coating (silk-screen) narrow-band filter can effectively eliminate the interference lights.
Existing narrow-band filters are completed by a coating process, and there is less light interference within 0 degrees-20 degrees. However, the available coating technology is not suitable for capturing signals at a large angle. There is a serious light interference if the angle is more than 20 degrees. Further, the current coating materials are special, and difficult to be processed.